This invention relates generally to organic rankine cycle systems and, more particularly, to an economical and practical method and apparatus therefor.
The well known closed rankine cycle comprises a boiler or evaporator for the evaporation of a motive fluid, a turbine fed with vapor from the boiler to drive the generator or other load, a condenser for condensing the exhaust vapors from the turbine and a means, such as a pump, for recycling the condensed fluid to the boiler. Such a system as is shown and described in U.S. Pat. No. 3,393,515.
Such rankine cycle systems are commonly used for the purpose of generating electrical power that is provided to a power distribution system, or grid, for residential and commercial use across the country. The motive fluid used in such systems is often water, with the turbine then being driven by steam. The source of heat to the boiler can be of any form of fossil fuel, e.g. oil, coal, natural gas or nuclear power. The turbines in such systems are designed to operate at relatively high pressures and high temperatures and are relatively expensive in their manufacture and use.
With the advent of the energy crisis and, the need to conserve, and to more effectively use, our available energies, rankine cycle systems have been used to capture the so called “waste heat”, that was otherwise being lost to the atmosphere and, as such, was indirectly detrimental to the environment by requiring more fuel for power production than necessary.
One common source of waste heat can be found at landfills where methane gas is flared off to thereby contribute to global warming. In order to prevent the methane gas from entering the environment and thus contributing to global warming, one approach has been to burn the gas by way of so called “flares”. While the combustion products of methane (CO2 and H2O) do less harm to the environment, it is a great waste of energy that might otherwise be used.
Another approach has been to effectively use the methane gas by burning it in diesel engines or in relatively small gas turbines or microturbines, which in turn drive generators, with electrical power then being applied directly to power-using equipment or returned to the grid. With the use of either diesel engines or microturbines, it is necessary to first clean the methane gas by filtering or the like, and with diesel engines, there is necessarily significant maintenance involved. Further, with either of these approaches there is still a great deal of energy that is passed to the atmosphere by way of the exhaust gases.
Other possible sources of waste heat that are presently being discharged to the environment are geothermal sources and heat from other types of engines such as gas turbine engines that give off significant heat in their exhaust gases and reciprocating engines that give off heat both in their exhaust gases and to cooling liquids such as water and lubricants.
In the operation of gas turbine engines, it has become a common practice to use an air conditioning system to cool the inlet air passing to the gas turbine in order to improve efficiency thereof during the warmer ambient conditions. It is also known to use the heat from the exhaust gases of a gas turbine engine in order to heat water for hot water heating. However, the demand for hot water heating during hot ambient conditions is limited while the demand for electric power often increases under those conditions.
Power generation systems that provide low cost energy with minimum environmental impact, and which can be readily integrated into the existing power grids or which can be quickly established as stand alone units, can be very useful in solving critical power needs. Reciprocating engines are the most common and most technically mature of these distributed energy resources in the 0.5 to 5 MWe range. These engines can generate electricity at low cost with efficiencies of 25% to 40% using commonly available fuels such as gasoline, natural gas or diesel fuel. However, atmospheric emissions such as nitrous oxides (NOx) and particulates can be an issue with reciprocating engines. One way to improve the efficiency of combustion engines without increasing the output of emissions is to apply a bottoming cycle (i.e. an organic rankine cycle or ORC). Bottoming cycles use waste heat from such an engine and convert that thermal energy into electricity.
Most bottoming cycles applied to reciprocating engines extract only the waste heat released through the reciprocating engine exhaust. However, commercial engines reject a large percentage of their waste heat through intake after coolers, coolant jacket radiators, and oil coolers. Accordingly, it is desirable to apply an organic rankine bottoming cycle which is configured to efficiently recover the waste heat from several sources in the reciprocating engine system.
While a bottoming cycle is useful in recovering waste heat from an engine, the applicants have recognized that an ORC is only capable of cooling engine intake air to ambient temperature, but for better efficiency, it is desirable to cool the intake air to temperature levels below ambient temperature.
It is therefore an object of the present invention to provide a new and improved closed rankine cycle power plant that can more effectively use waste heat.
Another object of the present invention is the provision for a rankine cycle turbine that is economical and effective in manufacture and use.
Another object of the present invention is the provision for more effectively using the secondary sources of waste heat.
Yet another object of the present invention is the provision for a rankine cycle system which can operate at relatively low temperatures and pressures.
A further object of the present invention is the provision for more effectively generating and using the energy of a gas turbine engine.
Still another object of the present invention is the provision for a rankine cycle system which is economical and practical in use.
Yet another object of the present invention is the provision for recovering waste heat from various sources and for obtaining increased efficiencies in an internal combustion engine.
These objects and other features and advantages become more readily apparent upon reference to the following descriptions when taken in conjunction with the appended drawings.